1. Field of the Invention
The system of the present invention relates to threaded pipe used in the oil industry. More particularly, the present invention relates to a System for accurately measuring the applied torque to a threaded connection between oilfield tubular products, such as drill collars, drill pipe, casing or other tubing, so that the pipe is threaded to the necessary torque.
2. General Background
In the field of oil and gas production, in recovery of the hydrocarbons from within the earth, the oil or gas is searched for (via drilling) and flowed to the surface through a plurality of sections of production pipe threaded end to end. These "strings" may be thousands of feet in length and include thousands of threaded connections. In order to properly assemble the strings, the sections are threaded together, and each adjoining section is torqued to a certain foot/pounds of torque to insure that the joint does not leak, which may result in having to pull the string out of the hole and repair or re-torque the joint or joints.
Although the reference has been to oil well casing, it should be made clear that the present system disclosed in this application applies to any threaded tubular members used in the oil field, where a certain torque needs to be achieved between the threaded members, and in fact, may apply to any use where threaded sections of pipe are used in industry.
In the state of the art of oilfield pipe connections, the torquing of these various connections is accomplished by the use of torque wrenches (manual or hydraulic) positioned around a joint to torque up the connection between the sections of pipe forming the joint. A cable or the like is run from the end of the torque wrench to a pulley apparatus which creates a pulling force on the wrench handle to in turn tighten the joint. In the case of a hydraulic power wrench (torque) a snub line or dead man line is positioned between one end of the wrench and a fixed object to prevent the wrench from spinning around the pipe as opposed to turning the pipe. A system is utilized, known in the art, whereby the amount of torque being applied to the pipe connection is recorded on a gauge, so that, theoretically, the operator knows the torque being applied. It is crucial that the operator know the amount of torque, so that he is assured that the threaded connection has been tightened sufficiently so as to avoid leakage down hole.
However, in the gauge's recordation of the torque as it is actually being applied to the threaded connection, an improper readout will occur if the angle between the cable and the wrench is anything other than 90 degrees. If the center line of the wrench is not perpendicular to the cable, forming an angle less than or greater than 90 degrees, then the force applied to the connection will be less than what is indicated on the gauge. By definition, if the force is less that what is indicated by the gauge, the pipe connection may not be completely tight and may result in leakage, damage, etc.
Several patents are identifiable which address the problem of the resolution of force when dispensed non-perpendicularly to the axis of a moment arm. These patents are more thoroughly identified in the Prior Art Submission, which will be submitted herewith.
Summary of U.S. Pat. No. 4,289,021, issued to Nelson, entitled "Tongs Having Torque Indicator Thereon" relates to an entire tong and although Nelson notes the significance of perpendicularity in the patent, he fails to address a resolution of the problem. As long as the Nelson force sensor is located in close proximity to the jaws (as opposed to the distal end of the lever arm), the angle problem is never encountered. If, however, a load cell were located at the distal end of the lever arm, it would only be accurate at 90.degree. since Nelson has made no provision nor claimed a method to correct for non-perpendicularity.
The Nelson patent further embeds a compression or tension load cell into the body of the tong, which would require substantial modification to existing tongs in use.
In U.S. Pat. No. 4,730,254, issued to Voden, Jr., entitled "Drill String Make-Up And Breakout Torque Control System And Apparatus", Voden distinguishes himself in the prior art as having made provision for the correction of vertical angle deviation. Voden utilizes a complex array of mechanical angle measuring devices, advising his computer of the various angles of forces, then has the computer calculate the perpendicular force. Voden, because of this complex method of calculating, would require an inordinate amount of time to compute the amount of torque being applied.
U.S. Pat. No. 4,137,758, issued to Rodland, entitled "Torque Indicator Apparatus" and U.S. Pat. No. 4,202,208, issued to J. Byrne, entitled "Hydraulic Torque Indicator" and U.S. Pat. No. 4,567,779, issued to P. Byrne, entitled "Method And Apparatus For Torque Monitoring" all involve mechanical angle correcting/measuring or controlling devices to resolve force, and thus ultimately determine the force perpendicular to the axis of the moment arm. These methods are slow, cumbersome and require substantial modification or addition to existing accepted equipment designs.
U.S. Pat. No. 4,501,335, issued to Gann, entitled "Method And Apparatus For Use In Drill String Make Up" involves the use of an optical or shaft encoder to determine the angle of pull which can then be used by a computer to calculate force. Such a design is slow and highly impractical since encoders are fragile electronic devices not generally intended for use in hazardous, harsh environments, such as the oilfield. Installation would require substantial modification and/or addition to existing tongs and undoubtedly meet with resistance in the field.